/*

   Derby - Class org.apache.derby.impl.sql.compile.RemapCRsVisitor

   Copyright 1999, 2004 The Apache Software Foundation or its licensors, as applicable.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */


package	org.apache.derby.impl.sql.compile;

import org.apache.derby.iapi.sql.compile.Visitable; 
import org.apache.derby.iapi.sql.compile.Visitor;

import org.apache.derby.iapi.error.StandardException;

/**
 * Remap/unremap the CRs to the underlying
 * expression.
 *
 * @author jerry
 */
public class RemapCRsVisitor implements Visitor
{
	private boolean remap;

	public RemapCRsVisitor(boolean remap)
	{
		this.remap = remap;
	}


	////////////////////////////////////////////////
	//
	// VISITOR INTERFACE
	//
	////////////////////////////////////////////////

	/**
	 * Don't do anything unless we have a ColumnReference
	 * node.
	 *
	 * @param node 	the node to process
	 *
	 * @return me
	 *
	 * @exception StandardException on error
	 */
	public Visitable visit(Visitable node)
		throws StandardException
	{
		/*
		 * Remap all of the ColumnReferences in this expression tree
		 * to point to the ResultColumn that is 1 level under their
		 * current source ResultColumn.
		 * This is useful for pushing down single table predicates.
		 */
		if (node instanceof ColumnReference)
		{
			ColumnReference cr = (ColumnReference) node;
			if (remap)
			{
				cr.remapColumnReferences();
			}
			else
			{
				cr.unRemapColumnReferences();
			}
		}

		return node;
	}

	/**
	 * No need to go below a SubqueryNode.
	 *
	 * @return Whether or not to go below the node.
	 */
	public boolean skipChildren(Visitable node)
	{
		return (node instanceof SubqueryNode);
	}

	public boolean stopTraversal()
	{
		return false;
	}

	////////////////////////////////////////////////
	//
	// CLASS INTERFACE
	//
	////////////////////////////////////////////////

}	
